Spark plug



Aug. 24, 1965 B. A. KNAGGS SPARK PLUG Filed Nov. 8, 1961 INVENTOR. BENJQMIN A. KNRGQS BY Mgo/v, SETTLE 6. (Jen/G Fla? United States Patent This invention relates to spark plugs for use in internal combustion engines, and more particularly to spark plugs of the flask-spark type in which the spark flashes over the surface of the insulator to ignite the mixture of gases in the engine cylinder.

Spark plugs of the flash-spark type differ from conventional spark plugs in that the spark, instead of jumping an air gap from the electrode to ground, flashes over a small portion of the surface of the insulator from one electrode to the other. 7

One of the objects of my invention is'to provide aspark plug of the flash-spark type having only a very small portion of the insulatorexposed to the combustion chamber, with the remainder of the insulator being sealed from the combustion chamber, to prevent overheating of the insulator but to maintain the' portion of the insulator within the combustion chamber and the ground ofthe insulator at a relatively high temperature to thus assist combustion. a

Another object of my invention is to provide a large electrode tip outside of the tip of the insulator to reduce the area of the insulator over which the spark must flash.

In the spark plug construction to be described, I have illustrated a specific construction for holding the insulator in the plug body. However, I do not wish to be limited to the specific construction because there are other means now being used successfullyfor accomplishing this purpose.

Other objects of this'invention will appear in the following description and appended claims, reference being had to the accompanying drawing forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawing:

FIGURE 1 is a side elevational view in section of one embodiment of my improved spark plug;

FIGURE 2 is a plan view of the inner end of the'spark plug of FIGURE 1; and

FIGURE 3 is a view of the firing end of a modified version of my spark plug.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring to the FIGURES 1 and 2, the shell forms a ground. Shell 10 is provided with a bore therethrough, having first inwardly tapered section 16 followed by a second outwardly tapered section 18. Section 18 terminates in inwardly tapered section 20. The tapered section 2%) is followed by a straight wall section 26 of reduced diameter, terminating at its inner end with a second straight wall section 27 of reduced diameter forming a shoulder for a gasket 28 to seat on. A wrench surface is provided on the upper end for threading the shell in the cylinder head.

An electrical insulator 5 is received in the shell 10. The insulator 5 is preferably fabricated from porcelain or the like. A bushing 6, which is of soft metal, is pressed down in bore 18. This operation expands the bushing 6 38 back into'the body of the insulator.

nites the fuel in the combustion chamber.

3,22,859 Patented Aug. 24, 1965 tightly against the insulator and shell bore and forces the insulator 5 against gasket 28 and shoulder on the bottom of the plug, thus sealing the insulator in the plug bore on taper 18 and gasket 23 and shoulder 27.

An electrical terminal 2 is threadingly received in the outer end of the insulator bore. The terminal 2 presses against a seal 32., preferably soft metal or the like, to seal the insulator bore. The terminal 2 has an axial opening 30 which receives one end of the electrode 25. Seal 32 is receiveed on the electrode 25. As will be noted, the electrode has a portion34 of reduced or tapered diameter whichcooperates with the inwardly tapering insulator bore portion 36 to lockingly engage the lower portion of the seal 32 when the seal is forced downwardly by threading of the terminal 2 or forcing seal 32 down by other means While at the same time holding the electrode 25 in place. This effectively fastens the electrode .in place and seals the electrode within the insulator.

As will be noted, the lower firing end 33 of the insu- 'lator 5 is considerably smaller than the remaining portion of the insulator and extends out of the shell 1t? and thus into the combustion chamber of the cylinder upon which the plug is mounted. A portion 49 of reduced diameter ofthe shell 16 also extends into the combustion chamber and closely around the small end 38 of the insulator 5. The electrode25 extends out of the insulator and has an enlarged portion 42. i

In the operation of theplug, when the applied electrical voltage reaches a predetermined value, a spark crawls from the electrode portion Hover the small end 38 of the insulator to the shell 10 which is grounded. The resultant electrical flash on the surface of the insulator ig- It will of course be appreciated that the insulator end 33 will become hot in use of the plug. The heat radiates from the small end of the shell portion 40 and insulator portion The insulator is sealed from the combustion chamber within the shell 10 and thus can absorb the heat of the hot end without becoming overheated itself as it receives no other heat from the combustion chamber. Heat is dissipated from the insulator to the shell 10 through the bushing 6 and th gasket 28 on the lower end of the insulator. i

The enlarged electrode portion permits reducing the area of the insulator over which the spark must travel. The small area over which the spark must travel reduces the overall resistance to sparking. It is preferred to enlarge the electrode tip rather than to increase the entire diameter of the electrode because increasing the entire diameter would require reducing the wall thickness of the insulator. This would weaken the insulator and lead to possible breakage thereof. In operation of the plug, the insulator end 38 becomes hot and this reduces the electrical resistance over the surface thereof to promote efiicient sparking action.

FIGURE 3 illustrates an alternate method of reducing the area of the insulator over which the spark must travel without enlarging the entire diameter of the electrode. In the FIGURE 3 construction, the reduced diameter firing end 44 of the shell is extended beyond the end surface 46 of the firing end 48 of the insulator. The end 44 is then spun over as at 49 to extend over the insulator end surface 46 towards the electrode 50. This construction also reduces the area of the insulator over which the spark must travel in its path between the electrode 5%) and shell end 44. As will be noted, the electrode 50 is extended beyond the end surface 46. The extending portion of the electrode is beneficial in extending the useful life of the spark plug by providing for more even electrode wear.

Having thus described my invention, I claim:

1. In a spark plug, a body having an insulator therein;

' sulator portion in the plug body, being small and the extension of said body,

both ends of said body being sealed, the lower firing end electrode in said insulator extending out of the small end of the insulator, the small end 'of said body acting as an electrical ground whereby the spark crawls over the walls of the insulator from the electrode to the small extension of said plug body causing an electrical flashing, the heat of the firing end radiating from the small end of said plug body and the small end of the insulator back into the insulator portion within the body of said plug, the inside of said body being sealed'to prevent overheating of said inthe end of the insulator the body being small to promote heating of these portions to an elevated temperature 'during operation of the plug, and an enlarged tipat the firing end of the electrode to reduce the area of the insulator over which the spark must fiash..

2; In a spark plug, an annular body with an exteriorly threaded end, a wrench engageable face on the body for threading the plug into an engine head, an insulator in said body sealed at both the upper and lower ends with said body, the lower firing end of said insulator being smaller than the portion of the insulator sealed within said lower firing end of the insulator extending through the seal in the lower end of the body to project into the combustion chamber of an engine cylinder, an extension on the lower end of the plug body extending closely around the firing end of said insulator and being turned slightly over the tip thereof to act as an electrical the firing end of the insulator, a portion of the electrode extending out of the firing end I of the insulator,

ground, an electrode at the portion of the plug body turned over the insulator tip reducing the surface of the insulator over which a spark must crawl from the electrode to create a flash to cause combustion of a fuel mixture in an engine cylinder.

'3. In a spark plug, a body having an insulator therein; both ends of said body being sealed, the lower firing end of said insulator being considerably smaller than the other parts of the insulator and extending out of said body to project into a combustion chamber, a reduced portion of the body extending intorthe combustion chamber and extending closely around the small end of the insulator, an

' electrode in said insulator extending out of the small end of the insulator, the small end of said body acting as ll an electrical ground whereby the spark crawls over the walls of the insulator from the electrode to the reduced portion of said plug body causing an electrical flashing, the heat of the firing end radiating from the reduced portion of said plug body and the small firing end of the insulator back into the insulator portion within the body of said plug, the inside of said body being sealed to prevent overheating of said insulator portion in the plug body, the end of the insulator being small and the extension of the body being small to promote heating of these portions to anelevated temperature during operation of the plug, and one of the tip of the firing end of the electrode and the small end of said plug body having a portion extending towards the other to reduce the area of the insulator over which the spark must flash.

4. A spark plug as defined in claim 3 and further characterized in that said insulator has a bore extending therethrough to receive the electrode, said elctrode having a variation in diameter intermediate the end thereof, said bore having an inwardly tapering portion adjacent the portion of the electrode having a variation in diameter, a relatively soft material received in the bore over the electrode in the space defined by the portion of the electrode having a variation in diameter and the inwardly tapering insulator bore portion, and means received in the bore in pressure engagement with the relatively soft material causing the soft material to seal the bore and mechanically fasten the electrode in place.

5. The device as claimed in claim 4 and further characterized in that the variation in diameter of the electrode comprises a reduced portion of the electrode diameter.

References Cited by the Examiner UNITED STATES PATENTS 1,420,159 6/22 Stephenson 313-131 2,267,571 12/41 McDougal 313145 X 2,272,558 2/42 Hall 3l3l30 X 2,356,104 8/44 Tognola 313145 X 2,760,099 8/56 Suter 313131 2,791,023 5/57 Stuermer 29-25 .12 2,874,322 2/59 Bychinsky 313-141 X 2,894,315 7/59 Candelise 29-25.12 2,900,547 8/59 Engel 313 2,906,908 9/ 59 Mallory -3 13144 2,989,660 6/61 Graham et a1 3l3--130 7 DAVID J. GALVIN, Primary Examiner.

ARTHUR GAUSS, JAMES D. KALLAM, Examiners. 

1. IN A SPARK PLUG, A BODY HAVING AN INSULATOR THEREIN; BOTH ENDS OF SAID BODY BEING SEALED, THE LOWER FIRING END OF SAID INSULATOR BEING CONSIDERABLY SMALLER THAN THE OTHER PARTS OF THE INSULATOR AND EXTENDING OUT OF SAID BODY TO PROJECT INTO A COMBUSTION CHAMBER, A REDUCED PORTION OF THE BODY EXTENDING INTO THE COMBUSTION CHAMBER AND EXTENDING CLOSELY AROUND THE SMALL END OF THE INSULATOR, AN ELECTRODE IN SAID INSULATOR EXTENDING OUT OF THE SMALL END OF THE INSULATOR, THE SMALL END OF SAID BODY ACTING AS AN ELECTRICAL GROUND WHEREBY THE SPARK CRAWLS OVER THE WALLS OF THE INSULATOR FROM THE ELECTRODE TO THE SMALL EXTENSION OF SAID PLUG BODY CAUSING AN ELECTRICAL FLASHING, THE HEAT OF THE FIRING END RADIATING FROM THE SMALL END OF SAID PLUG BODY AND THE SMALL END OF THE INSULATOR BACK INTO THE INSULATOR PORTION WITHIN THE BODY OF SAID PLUG, THE INSIDE OF SAID BODY BEING SEALED TO PREVENT OVERHEATING OF SAID INSULATOR PORTION IN THE PLUG BODY, THE END OF THE INSULATOR BEING SMALL AND THE EXTENSION OF THE BODY BEING SMALL TO PROMOTE HEATING OF THESE PORTIONS TO AN ELEVATED TEMPERATURE DURING OPERATION OF THE PLUG, AND AN ENLARGED TIP AT THE FIRING END OF THE ELECTRODE TO REDUCE THE AREA OF THE INSULATOR OVER WHICH THE SPARK MUST FLASH. 